Diamonds from Marange were conditionally approved for Kimberley Process certification at a meeting hosted in St Petersburg last month by the World Diamond Council.

Government sources revealed Grace Mugabe has a large holding in Mbada Diamonds together with little known South African company, Grandwell Holdings, and the Zimbabwe Mining Development Corporation, according to The Zimbabwean newspaper.

“The First Lady is one of the shareholders in Mbada Diamonds,” said an official from the ministry of mines cited by the newspaper.

The official said Grace Mugabe had held many meetings with Robert Mhlanga, Mbada Diamonds' chairperson. He is said to be a close confidant of the Mugabe family dating to when he served as President Mugabe's personal helicopter pilot.

Mbada Diamonds last year flew more than 300,000 carats of diamonds to Harare International Airport where it planned to auction the gems, but the sale was stopped shortly before it was due to take place.